samedi 18 octobre 2014

The Westland Whirlwind, an outstanding fighter suffering from breach of faith from the RAF staff (revised 29 / 10 / 2017)

Wanted: A fighter with a real punch...

It is likely that, in 1934, after the successful trials of the French Dewoitine D 501 fighter fitted with the moteur-canon Hispano-Suiza 12 X Crs, the British deciders began to be worried with the possibility than a few fighters could be able to destroy easily the aircrafts of the Bomber Command.  

The actual Hawker Fury II fighters (of rather similar performances) were fitted only with 2 riffle caliber machine guns (muzzle velocity of 744 m/s & 250 rounds, each bullet weighting ~0.011 kg).

The first response of the British Air Staff was to increase the number of machine guns up to 8 as also to use of very better Browning M 2 MG of the same caliber (muzzle velocity of 850 m/s). So was the armament of the Hurricane Mk I and Spitfire Mk I.

But some undoubtedly very advanced twin-engined fighters (Potez 63 and Messerschmitt Bf 110) appeared in 1936 with 2 cannons in the nose. 

Appearing as a British answer, a program (F 37/35) was published in 1935 by the RAF staff, requiring a twin-engined fighter fitted with 4 efficient 20 mm cannons.

The very good work of Teddy Petter

The winner of the contest was the Westland Whirlwind designed by Teddy Petter. 

The layout of her airframe achieved a spectacular fineness and each detail revealed as thoroughly conceived: This aircraft was a very promising fighter issued from exceptional aerodynamics studies.

Several Whirlwind flying at low-medium altitude

This fighter was not much larger than a Hawker Hurricane (a lenght ofless than 10 m and a wingspan of a bit more than 13 m)

The structure was totally metallic, with duraluminium stressed skin.

The narrow monocoque fuselage, made of magnesium, was rather cylindrical with a cockpit canopy rather similar to that of the French Nieuport 161 fighter in 1936.

The tail had the horizontal stabilizer mounted very high on the vertical tail.

The wings totaled 23.2 square meter, 0.7 m² less than the Hurricane Mk I (!) and was fitted with Fowler flaps.

The empty weight was 3,770 kg and the weight increased to 4,660 kg for take off (Whirlwind I, i.e. fighter only), so the wing loading was 200 kg/m².

The engines nacelles were very well streamlined and the engines were two Rolls-Royce Peregrine, last variant of the well known Kestrel. 

Each of these engines had a displacement of 21 liters and delivered 880 hp at 3,000 m (10,000 ft) using octane 100 fuel. The dry weight of one engine was 520 kg.

The chosen armament was one of the strongest of all the WW II fighters: Four Hispano-Suiza HS 404 20 mm cannons gathered in the nose. 

That was much more than twice the armament of the Messerschmitt Bf 110, which had only 2 MG FF Oerlikon cannons. 

The Hispano -Suiza 404 had a muzzle velocity of 880 m/s, 280 m/s faster than the MG FF, each shell weighting 130 gram. 

So, its ballistics was very better and its kinetic energy was at least, twice that of the Swiss cannon.

The first flight of the Whirlwind occurred on October 11, 1938.

The top speeds of the Westland fighter were:
  • 500 kph at 1,500 m,
  • 540 kph at 3,000 m,
  • 580 kph at 4,500 m, some 20 kph better than the Spitfire Mk I at this altitude (one may also compute that, with 720 hp Kestrel engines, this top speed would drop to 525 kph)
The climbing ability was good:
  • 3,000 m in 4' 00",
  • 6,000 m in 8' 30" (one minute faster than a Hurricane Mk I).
These climb times were similar to those of the Hawker Typhoon which was only 10 kph faster at 15,000 ft, but much more faster at both lower and higher levels.
The service ceiling was a bit more than 9,000 m, a rather disappointing performance, but the logical consequence of a weak supercharger.

The stall speed of the Whirlwind was on the high side (153 kph), nevertheless, her maneuverability was outstanding, especially because her ailerons were much more efficient and pleasant than those of the actual Spitfire Mk I at high speed.

Four hundreds of Whirlwind (two series of 200) were ordered in January 1939.

The first productions fighters were delivered in June 1940 to 25 Squadron, a night fighter unit, but they were removed and transferred in July 1940 to the 263 Squadron which was in total reformation after having lost 10 pilots (among them were the 3 officers commanding the unit!) in the sinking of the Glorious carrier, at the end of the Battle of Norway.

The Westland Wirlwind production was slow essentially because Rolls-Royce had not finished its Peregrine engine, and so, delivered them at very slow tempo.

In action...

If you expected to have an idea of the capacities of the Whirlwind against the Luftwaffe during the Battle of Britain - because the first productions fighters were delivered in time - forget it: On October 17, 1940, Air Chief Marshall Hugh Dowding forbade any apparition in the Battle of the 263 Squadron, and, today, we don't know if his decision was motivated by problems linked to the fighter or to an insufficient formation of the pilots (or both..).

Latter, the 263 Squadron moved to Exeter and was, at last, operational the December 7, 1940. 

Most of her job was to destroy the German E-Boats used to rescue the crews of the bombers damaged by the RAF. 

The first aerial engagement occurred the January 12, 1941 and was against a Junkers 88 which was probably downed in the Western Approaches.

After this victory, the Whirlwind  obtained numerous others victories against Ju 88, Dornier 217, Messerschmitt Bf 109 and Bf 110, during Rhubarb missions over English Channel, Northern France and Belgium.

She was also used to escort 54 Blenheims gathered to destroy power stations near Cologne the August 12, 1941. 

Owing to their 500 km combat radius, the Whirlwind were forced to turn back at Antwerp. 

Ten bombers (less than 20%) were lost, such losses being negligible compared to those of Allied bombers (from 30 to 90%) during the Campaign of France in May-June 1940.

At low altitude, the Whirlwind was extremely efficient against the German fighters.

She was very efficient too against small ships and a lot of terrestrial targets, as locomotives, tanks and so on, demonstrating the heavy punch of her armament.

The 137 Squadron was the only other one to be Whirlwind equipped (since September 1941). It used the fighter to drop 125 or 225 kg bombs.

The 263 Squadron also used of the bomber variant, including in dive, as they had done from October 24 to November 26, 1943, against the German blockade runner Münsterland in dry dock at Cherbourg.

With 12 Whirlwind, they dove from an altitude of 3,600 m down to 1,500 m, facing a very strong Flak fire. 

The bomb impacts were quite all in a circle having a diameter of 150 m. 

Only one Whirlwind was lost. 

One may highlight that such a dive induced necessarily a strong acceleration but the pilots never complained about handling difficulties. 

One may underline the soundness of this fighter, very difficult to destroy for her enemies and very protective for her pilots.

The November 29, 1943, the RAF decided to equip the pilots of both squadrons with Hawker Typhoon.

I'm not sure that was a wise decision: The Hawker fighter was not better adapted to high altitude flying than the Whirlwind, she was less maneuverable and her Napier Sabre engine was even less reliable than the Rolls-Royce Peregrine...

Overwhelmed Rolls-Royce engineers ?

Knowing the great area of competence gathered in the Rolls-Royce company, the problems which plagued the Peregrine engine may be seen as amazing.

This engine was nothing more than a boosted Kestrel, differing by an adaptation to the 100 octane fuel and by its HM Hobson carburetors, fitted behind the engine to allow more space for the supercharger, and, theoretically, giving a more efficient mixture. May be, these devices have been chosen to profit from the automatic Hobson boost pressure regulator (source: Flightglobal / Archive). 

However the Peregrine lost quickly its power above 6,000 m and had overheating problems (due to formation of vapor bubble in the liquid cooling circuit when used too long at full power) and probably other ones. 

At that very moment, the Rolls-Royce company was, simultaneously, developing 4 other aeronautical engines: The Vulture (a twin Peregrine in X), the Exe (another X-24 engine), the Griffon (derived from the R of the Schneider Cup) and, obviously, the famous Merlin. A very heavy task!

Very early, the Rolls-Royce staff expressed the wish to abandon the Peregrine engine. 

May be, such a wish influenced the RAF deciders who decided to stop the construction of the Whirlwind

Was it the good decision? I'm not convinced at all, because: 
i) Most of the problems encountered were likely easy to solve (for example, the vapor bubbles could likely be eliminated by fitting degassers in the liquid cooling circuit). 
ii) The compressor problem would be solved by changing the actual device for another.
iii) Solving these problems could have good consequences on the Vulture finishing (amazingly, the Vulture was proposed for the Hawker Tornado before the Peregrine was, at least, completely reliable). It seems not to be a good method.

From the other hand, a lot of work was spent by the company to finish the Griffon. 
Nevertheless, this powerful engine was operational primarily in Spring 1943 with the Spitfire XII, and mainly, but too late, in mid-1944, with the Spitfire XIV, at the very moment the piston engines were losing their supremacy in favor to jet reactors and the Merlin appeared to achieve quite similar performances (Merlin 130/131 fitted on the De Havilland Hornet) without the same handling difficulties. 

True shortcomings

However, as any other aircraft, the Whirlwind was not perfect. 

A range problem?

It was written that the most impeding characteristics of the Wirlwind was her rather short autonomy, but this data is not easy to obtain. 

Green, in Fighters #2, gave only the information of an escort flight "as far as Antwerp..."

The same author, associated with Swanborough, in The Complete Book of Fighters, gave a total flight time of 1 hour and 15 minutes, translatable to 725 km at the top speed of 580 kph (not very consistent with the overheating at full speed) or 512 km at 410 kph (50 % of the power - an unrealistic value) . 

In the Wikipedia in English article on this fighter (October 15, 2014) you may found two other values: 
  • In the text, the combat radius was given as ~480 km. 
  • But, in the specifications, the total range is published as 1,288 km (an amazingly precise data!), but, at low level, the combat radius was 240 km, with normal reserves. 
These last data appear as the more likely, but underline how heavy was the fuel consumption at low level (twice the "normal" one).

So, the autonomy of the Whirlwind was of the same order of magnitude than those of Potez 631 and Messerschmitt 110 twin engined fighters.

OK, her range was half of those of the Bristol Blenheim Mk I F, but the Whirlwind was a true fighter, not the the Blenheim (the night fighting being a completely different task).

It seems that nobody want to fit some jettisonable tanks on the Westland Whirlwind

The idea of jettisonable tanks was invented by German for the Messerschmitt 109 E 7 in Fall 1940.

Such a device could have given a clearly better range, enabling the escort of the aircrafts of the Bomber Command to strike at daylight the German target with reduced losses, allowing them a much more military and economic impact.

Useless as a cannon fighter? 

The English Wikipedia article (October 17, 2014) on the Whirlwind is often excellent.

However, the authors wrote that, since the appearance of the Spitfire I B (with 2 Hispano-Suiza HS 404 cannons) during the Summer of 1940, the RAF did not have any more need of the Whirlwind

May be, these authors had completely forgotten the Spitfire story!  

The very thin wings of the Spitfire I were not conceived to withstand the strong efforts occasioned by the fire of such powerful weapons. So, they jammed quickly when fitted with HS 404 cannons.

Supermarine resolved the problem with the universal or "C" wing introduced operationally clearly later on the Spitfire V C, at the end of 1941, very, very later!

Another motivation may be the awaited delivery of the first Lockheed P 38 fighters (whose first flight was done the January 27, 1939). 

Lockheed, very optimistically - as usual with this company - claimed a top speed of 640 kph (400 mph), 60 kph faster than the Whirlwind. 

But the Lightning to be delivered did not fulfill her promises. 
  • Deprived of her turbo-superchargers (by order of the US Congress), she was not so fast. 
  • With her 2 engines running the same direction, the P 38 was very difficult to handle. 

  • Owing to her weight of 6,140 kg, her maneuverability was, at least, very questionable.
Justifiably, the RAF refused these P 38.

Consequently, the RAF pushed for the service entry of the Typhoon, long before her teething troubles were eradicated (23 pilots lost their life after tail losses, a problem solved only at the end of 1944!). 

My (very) iconoclastic solution...

There was two parts of a true solution, easy to use since 1939.

The first part was to eliminate 2 canons (each HS 404 cannon weighting 48 kg + 25 kg for the drum with 60 shells), allowing space storage for ~200 litters of supplementary fuel.

The second part of the solution (unacceptable for English deciders ;-)) was to replace the Peregrine engines by French Hispano-Suiza 12 Y 29 engines of 810 hp for take off and 920 hp at 3,600 m. 

This engine had a dry weight of 475 kg (source: Danel & Cuny, Le Dewoitine 520, Docavia #4), allowing a total gain of 90 kg. 

Such a solution could allow a top speed of 590 kph at 5,000 m, an elongated combat radius and more diverse missions...

Some lessons...

The December 18, 1939, three squadrons of Vickers Wellington (22 bombers) were sent to bomb some the Wilhelmshaven facilities and shipping. 

The distance between Great Yarmouth in East-England and Wilhemshaven in Germany is a bit less than 450 km. 

No actual RAF fighter was able to escort these bombers. 

If someone wanted to use of Spitfire Mk I, they would need to land in the Netherlands for refueling!

So, 12 of these British bombers were downed and 3 others were badly damaged by a group of Messerschmitt Bf 110.

The British staff take this event into account and preferred to use his bomber for night bombing.

Nevertheless, such an escort duty was possible for the Whirlwind without any supplementary tank, allowing her ~15 minutes of combat. 

It is quite obvious the Westland fighter was superior to the Bf 110 because she was 40 kph faster, more nimble (~2,000 kg lighter) and she had a very stronger punch.

Neglected for such missions, the Whirlwind was used without neither strategic nor even tactical imagination, as if the RAF deciders have not read her handbook.

During the Battle of Britain, the same deciders used of their very poor Blenheim Mk I F or Mk IV F, with a top speed of 420 kph at ~3,700 m, a climbing time to 4,500 m of 15 minutes, a take off weight of ~6,500 kg, an armament of 5 forward firing riffle cal. machine guns. 
These characteristics explained perfectly the massacre (44 losses) they suffered during the Battle of Britain.

The only good news was a total range of 2,200 km and sufficient room to embark a radar.

OK, the appearance of the Beaufighter was a relief to the British night fighting. 

A top speed of 520 kp at 4,500 m, a service ceiling of ~8,600 m and 4 Hispano 20 mm cannons were obtained. 

But the take-off weight increased to 9,000 kg, only 450 kg less than the Boulton Paul Hampden bomber...  

The Whirlwind was, undoubtedly, a very better fighter. 

The first proof was simple: The last British piston-engined fighter, the gorgeous De Havilland Hornet, was a transposition of the radical ideas expressed in the Whirlwind, with a more sexy shape.

The second proof of the excellence of the concepts developed by Teddy Petter was the Whirlwind can fly over German occupied territories during 3 long years of war without any real modification.

She as all qualities to fulfill a lot of task and her survivability was one famous asset.

She needed only a better Air staff...

2 commentaires:

  1. Hi,
    You wrote "From the other hand, a lot of work was spent by the company to finish the Griffon.
    Nevertheless, this powerful engine was operational too late (in mid-1944, with the Spitfire XIV)".

    The Rolls Royce Griffon made the first operational sortie of the Spitfire MkXII in April 1943,more than one year sooner.

    1. Hi, Dan,

      You are right, indeed.
      I may explain this inaccuracy: In my mind, the Mk XII was an interesting link between the MK V C and the Mk XIV.

      The Mk XIV was the most produced Griffon-powered Spitfire (~ 1,000 examples) and also she have got the rare honor to down Me 262 jets: An unbeatable calling card!

      Nevertheless, Supermarine had to work one year to improve the Mk XII...